Chair backrest support



FIG. 1 is a perspective view of a first embodiment of the chair backrest support showing our new design;

FIG. 2 is a side elevational view of thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a perspective view of a second embodiment of the chair backrest support;

FIG. 5 is a side elevational view thereof; and,

FIG. 6 is a rear elevational view thereof.

The dashed lines within the figures are for illustrative purposes only and form no part of the claimed invention. 

The ornamental design for a chair backrest support, as shown and described. 